Submarine landslide recurrence and links to seismicity on the Gorringe Bank Seamount, Offshore Portugal

Submarine landslides are common features occurring on the flanks of seamounts. Often triggered by earthquakes or volcanic activity, such landslides are potential generators of tsunamis that constitute a dire geohazard for coastal communities. Understanding the recurrence history and geomorphology of seamount-flanking landslides and their link to seismic triggers is crucial for tsunami hazard assessment. This work aims at revealing the recurrence history of the landslides on the Gorringe Bank and their role on regional geohazards. Morphologically, the Gorringe Bank is the largest submarine seamount in Europe, with a length of circa 180 km and a height of 5000 m. It is linked to NW-directed thrusting which led to the exhumation of upper mantle lithologies in this major bathymetric structure. Numerous landslide scars are identified on both its northern and southern flanks, yet there is limited evidence of their presence and morphology on modern bathymetric data. A wealth of 2D seismic reflection profiles from offshore Southwest Portugal is here used to analyse the occurrence, timing and morphology of landslides complexes on the northwestern flank of the Gorringe Bank. A widespread frontal landslide complex of approximate Upper Miocene age is present along the whole flank, likely associated with the main phase of uplift. However, the recurrence of expressive submarine landslides in the Plio-Quarternary sequence is generally focused towards the northern segment of the Gorringe Bank. The geographical correlation between the areas of higher landslide number and clusters of seismicity epicentres suggest a close link between the two. This has direct implications for the assessment of landslide-prone locations on the seamount and to regional tsunami hazard models applicable to the Iberian and Northern African margins.

This work is supported by the FCT funded project MAGICLAND - MArine Geo-hazards InduCed by underwater LANDslides in the SW Iberian Margin (Ref: PTDC/CTA-GEO/30381/2017),